Flexible coupling 910001. Commonly referred to as 4". Fits between gearbox output flange and shaft coupling to allow for any temporary misalignment caused by flexing of boat structure or movement of engine on its mounts. Failsafe included. Mounting: 4x M10 bolts, 3.25" PCD. Register: 63.5mm (2.5"). Typical application: Use with RD202153 or RD202165 split couplings.